| 摘要 |
In order to use one dispersion compensating fibre element for selecting a given value of dispersion, one or more frequency or wavelength dependent optical reflection gratings (G 1 , G 2 , G 3 ) is located at such a position along the unit 8 that the double traversal of a section results in a desired value of dispersion at a frequency. A directional coupler 9 diverts the reflected wave to utilisation means 10 for its recovery. If a different value of dispersion at the same wavelength, or if some value of dispersion at a different frequency, is required, a reflection grating effective to reflect at the appropriate frequency and at the appropriate position, gives the required values.
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